Right! I have a pic of ethane and ethene in front of me, but I dont understand something.
With ethene, if you break a bond, that means you can put a hydrogen on the end right? And then if you break the bond left in the middle, you can put another hydrogen on. But then there is no bond left in the mdidle to connect the 2 carbon atoms :| Ive always had trouble with this Help please, someone

Ethene has a double bond
in polymerisation or other such processes, the double bond will become a single bond. When this happens, there is a bond leftover, whcih is used to connect the molcule to another carbon atom.

That's the basic principle. What i do not understand is what you are talking about. Sorry if i am slow or whatever........

Can you make it more clear as to what you do not undestand, or post the link to the image

What im saying is, if you have a double bond, to get it back to alkane form, you need to break that bond, right? Which means you need TWO new hydrogen atoms.
If you break off one 'arm' of the double bond, you can shove one hydrogen atom on that, but you need 2. So if you break the other arm thats left, what is left ot connect the carbon atoms? hmmm! hehe

it might help to know that carbon can make 4 bonds.... but dont try and understand it properly- GCSE revision guides oversimplify everything. i like to try and write it out as a list of points- sometimes it makes more sense that way.

I looked at my revision guide- basically- you break the bond of the first molecule- you only need one free bond on the right- this attaches to the next molecule which has a free bond which attaches to the next one and so on- each consecutive one just has one free bond- but it only needs one- because the second bond came from the one free bond of the molecule before it- does that make any sense?

(Original post by butterfly_girl_5)
it might help to know that carbon can make 4 bonds.... but dont try and understand it properly- GCSE revision guides oversimplify everything. i like to try and write it out as a list of points- sometimes it makes more sense that way.

I looked at my revision guide- basically- you break the bond of the first molecule- you only need one free bond on the right- this attaches to the next molecule which has a free bond which attaches to the next one and so on- each consecutive one just has one free bond- but it only needs one- because the second bond came from the one free bond of the molecule before it- does that make any sense?

yeah it sorta does! God damnit, I need those things that you play with to make one for myself and see. it would really help if someone could draw a pic- this is bugging me :P

It's because they are joined together. They just offer one new bond, which kind of joins on to the next one. So the first monomer at the end has one spare bond (as one is used to join the Carbons together), which joins on to one hydrogen atom; then the next monomer has one free bond which joins on to the end of the previous one... do you get that?

when the H2 molecule approached the double bond it gets polarised
the slightly positive hydrogen breaks the H-H bond (by giving the shared pair of electrons to the other hydrogen)
the slightly +ve hydrogen makes a bond with one of the carbons in ethene
you are then left with a carbocation.... the other hydrogen is now negatively charged (has a lone pair of electrons)
so this hydrogen bonds with the positive carbon.... using those electrons

(Original post by Excalibur)
It's because they are joined together. They just offer one new bond, which kind of joins on to the next one. So the first monomer at the end has one spare bond (as one is used to join the Carbons together), which joins on to one hydrogen atom; then the next monomer has one free bond which joins on to the end of the previous one... do you get that?

ahhh..
so you mean instead of actually adding hydrocarbons on, they just sort of join with other monomers to form polymers?